a) Field of the Invention
The present invention relates to a torsion damper for a clutch disc, and more particularly, it relates to a torsion damper for a clutch disc for elastically coupling at least two portions of a clutch disk.
b) Description of the Related Art
A clutch disc is used, for example, in a clutch disc assembly which is positioned between an engine and a transmission in an automobile. The clutch disc has a clutch plate and a retaining plate working as a power input rotating element, a spline hub working as a power output rotating element, and an elastic element for elastically coupling both of them.
For the elastic element, generally, a coil spring (torsion spring) is used, and is usually disposed in window holes formed in each of the power input and output rotating elements. Torque from the clutch plate and the retaining plate is transmitted from end surfaces of the window holes in the plates via the torsion spring to the spline hub. During power transmission, the torsion spring is compressed and may expand in a direction of the rotation absorbing vibrations and fluctuations in the power transmitted in response to relative rotary displacement between the clutch plate and the retaining plate.
Alternatively, in some clutch discs, a single block of torsion rubber is used with the coil spring, serving as an additional elastic element to optimize torque transmission and vibration dampening. The torsion rubber is positioned concentric with the torsion spring and is comprised of a rubber element capable of expanding and contracting in a direction of rotation in response to relative rotary displacement between the power input and output rotating elements. In some clutch discs, seat elements are provided at opposite ends of the rubber element and made of hard material such as resin. One end surface of each seat element works as a contact surface in contact with either the clutch plate or the retaining plate while the other end surface is coupled to an end of the rubber element.
The torsion rubber is compressed similar to the torsion spring, and in this situation, the rubber element tends to expand outward in radial directions. The seat element and the rubber element sometimes distort relative to each other in radial directions in the clutch disc corresponding to relative torsional movement between the power input and output rotating elements. In such a case in the prior art arrangement, since shearing force works in an adhesion surface where an end surface of the rubber element adheres to the seat element, the rubber element may crack or the adhesion surface may be broken off. Especially after a long term of use, fatigue failure due to repetitive compression may arise in the vicinity of the contact surface.
In the prior art arrangement, an adhesion step is required in a fabricating process, and this leads to an increase in fabrication cost. Moreover, since adhesion strength must be attained to a specified extent, this results in materials of the rubber element and seat element being restricted, and a material cost may increase.